Method of making luminance enhancement optical substrates with optical defect masking structures

ABSTRACT

An optical substrate possesses a structured surface that enhances luminance or brightness and reduces the effects of structural defects on perceived image quality. User perceivable image cosmetic defects caused by manufacturing or handling, can be masked by introducing structural irregularities in the optical substrate, which may be non-facet flat sections or in-kind to the defects. Optical defects caused by non-facet flat sections in the prism structure of the optical substrate (e.g., flat-bottom valleys with a certain valley bottom thickness above the base layer, and/or flat-top peaks, and/or openings in the optical substrates that expose flat sections of underlying base layer) can be masked by providing distributed in-kind non-facet flat sections (e.g., flat-bottom valleys, and/or flat-top peaks, and/or openings exposing sections of underlying base layer), to diffuse the prominence of the original defects with the introduced irregularities.

This application claims the priority of U.S. Provisional Application No.60/818,044, filed Jun. 30, 2006. This document is fully incorporated byreference as if fully set forth herein.

The publications noted in the disclosure herein are each fullyincorporated by reference, as if fully set forth in its entirety herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to optical substrates having a structuredsurface, particularly to optical substrates for brightness enhancement,and more particularly to brightness enhancement substrates for use inflat panel displays having a planar light source.

2. Description of Related Art

Flat panel display technology is commonly used in television displays,computer displays, and handheld electronics (e.g., cellular phones,personal digital assistants (PDAs), etc.). Liquid crystal display (LCD)is a type of flat panel display, which deploys a liquid crystal (LC)module having an array of pixels to render an image. In backlight LCDs,brightness enhancement films use prismatic structures to direct lightalong the viewing axes (i.e., normal to the display), which enhances thebrightness of the light viewed by the user of the display and whichallows the system to use less power to create a desired level of on-axisillumination.

Heretofore, brightness enhancement films were largely provided withparallel prismatic grooves, lenticular lenses or pyramids on the lightemitting surface of the films, which change the angle of the film/airinterface for light rays exiting the films and cause light incidentobliquely at the other surface of the films to be redistributed in adirection more normal to the exit surface of the films. The brightnessenhancement films have a light input surface that is smooth, throughwhich light enters from the backlight module.

Heretofore, brightness enhancement films are made up of two layers,including a support base layer and a structured layer. FIG. 1 depicts asectional structure representative of prior art brightness enhancementfilms. The brightness enhancement film 100 includes a base layer 102made of polyethylene terephthalate (PET), and a structured layer 104 ofprism structures made of acrylic, which function to redirecting light.

The structured surface of brightness enhancement film 100 is formedafter bonding a layer of materials (e.g., an acrylic or polycarbonatelayer) to the base layer 102 prior to forming the prism structures inthe acrylic layer to form the structured layer 104. The prism structuresin the structured layer 104 may be formed using a number of processtechniques, including micromachining using hard tools to form mastermolds or the like for forming the prism structures. The hard tools maybe very small diamond tools mounted on CNC (Computer Numeric Control)machines (e.g. turning, milling and ruling/shaping machines), such asknown STS (Slow Tool Servo) and FTS (Fast Tool Servo). U.S. Pat. No.6,581,286, for instance, discloses one of the applications of the FTSfor making grooves on an optical film by using a thread cutting method.The tool is mounted onto the machine, to create longitudinal prisms in aplane. The mold may be used to form the structured layer through hotembossing a substrate, and/or through the addition of an ultravioletcuring or thermal setting materials in which the structures are formed.

As shown in FIG. 1, the bottom of the valleys 106 of the prisms in thestructured layer 104 is not at the surface of the base layer 102, butspaced at a distance d from the contacting surface of the base layer byacrylic material. In general, the valley bottom thickness d rangebetween 0.3 to 3 micrometers. In order to obtain the bottom thickness,several parameters must be controlled during the curing process to formthe structured surface. It has been found that due to inherentlimitations during manufacturing processes (including the mold formingprocess and the structured surface forming process), it is challengingto control a consistent valley bottom thickness d. As noted in theearlier filed U.S. patent application Ser. No. 11/635,802 (which isincorporated by reference herein), unwanted optical cosmetic defectssuch as ‘chatter’ and/or non-uniformity of the brightness enhancementfilm are introduced as a result of non-uniformity in the valley bottomthickness in the structured layer. This results in a phenomenon that iseasily seen for existing brightness enhancement films, in which repeateddark shades/lines are seen from the planar light source transmittedthrough the brightness enhancement film.

The valley bottom thickness can be completely missing (i.e., withoutresin above the base layer, exposing the base layer) at some locationsin the structured layer, as a result of defects introduced by themanufacturing processes, as affected by, for example, the manufacturingconditions, environmental specifications and handling processes. Thelocations with missing valley bottom thickness create optical cosmeticartifacts in the displayed image which are perceivable to a naked eye,such as white spots and white lines in the display image. The artifactsare perceivable because of the high contrast between the exposed baselayer and surrounding unexposed areas. For example, a white line defect(see FIG. 1 at 108) is the result of a gap (e.g., 5 μm wide by 620 μmlength) of no valley bottom thickness between two prisms, which may becaused by the replication process using the mold. A white spot defect(see FIG. 1 at 109) is the result of a spot (e.g., a 8 μm by 20 μm to 15μm by 40 μm hole, or even larger 20 μm by 70 μm hole) of no valleybottom thickness at a spot along a valley, which may be caused duringreleasing the structured layer film from the mold, as resin (e.g.,acrylic) was left on the surface of the mold. Other defects may includea row of holes lined up to result in a white line defect in thedisplayed image viewed by the naked eye.

On the other hand, careless handling may damage the peaks, valleysand/or facets of prisms, for example, by scratches or cutting marks.Other physical conditions and structural deficiencies may also exposethe base layer and/or damage prism peaks, valleys and/or facets, forexample, cracks and indentations in the structured layer, and foreignparticles or materials introduced during molding process butsubsequently released from the structured layer.

The push to improve image quality elevates the cosmetic requirements ofluminance enhancement optical substrates. A viewer may easily perceiveeven very small isolated defects. To overcome the optical cosmeticdefects noted above, several approaches have been attempted. Onesolution is to provide a very clean room and use extraordinary care inthe manufacturing process, and employ extremely critical quality controlprocedures. This will significantly decrease throughput, and also highlyincrease production costs. Another solution is to provide a diffuser tothe display. Diffusers with matte structures may mask many of thedefects and increase the production yield. This solution, however,increases the components used and enlarges the volume and weight of thedisplay.

What is needed is an optical substrate structure that both enhancesbrightness and reduces the effects of structural defects on perceivedimage quality.

SUMMARY OF THE INVENTION

The present invention is directed to a luminance enhancement filmcomprising an optical substrate (which may be supported by a base layer)that possesses a structured surface that enhances luminance orbrightness and reduces the effects of structural defects on perceivedimage quality. In accordance with the present invention, userperceivable optical cosmetic defects caused by manufacturing or handlingcan be masked by introducing defined structural irregularities in theoptical substrate. The optical cosmetic defects would be blended withthe optical effects introduced by such structural irregularities, withthe cosmetic defects reduced in prominence in the display image, toeffectively hide, mask or largely reduce certain cosmetic defects.

In one aspect of the present invention, the pre-defined irregularitiesintroduced may be in-kind to the anticipate defects. In one embodimentof the present invention, optical defects of the type comprisingnon-facet flat sections in the prism structure of the optical substrate(e.g., flat-bottom valleys with a certain valley bottom thickness abovethe base layer, and/or flat-top peaks, and/or openings in the opticalsubstrates that expose flat sections of underlying base layer) can bemasked by providing distributed in-kind irregularities having definednon-facet flat sections (e.g., flat-bottom valleys, and/or flat-toppeaks, and/or openings exposing sections of underlying base layer), todiffuse the prominence of the original defects with the introducedirregularities. The in-kind irregularities introduced may not need to beof the exact same type, number, shape and size as the original defects.For example, openings (e.g., holes or gaps) in the optical substrateexposing flat sections of the underlying base layer, or flat-bottomvalleys, or flat-top peaks, may be masked by at least one of flat-bottomvalleys and/or flat-top peaks and/or openings exposing flat sections ofunderlying base layer. If the defects are other than non-facet flatsections noted above, the in-kind irregularities intentional introducedinto the optical substrate would likewise take on in-kind attributesother than non-facet flat sections.

In another aspect of the present invention, regardless of theanticipated defects, the irregularities introduced may simply be definednon-facet flat sections (e.g., flat-bottom valleys, and/or flat-toppeaks, and/or openings exposing sections of an underlying base layer).The non-facet flat-sections of the irregularities may still mask othertypes of defects found on the prism structure of the optical substrate,such as made by, for example, scratches, cutting marks, cracks,indentations and/or other unintended structural defects in the prismstructure, and/or foreign particles or materials introduced duringmolding process, which may or may not be subsequently released from theprism structure. The defects may be found anywhere on the prismstructure (e.g., prism peaks, valley and/or facets, and/or underlyinglayer, if present, which supports the optical substrate).

The predefined irregularities introduced may be distributed across theoptical substrate in an orderly, semi-orderly, random, or quasi-randommanner. The predefined irregularities introduced may not mask all typesof defects present in an actual luminance enhancement substrate. Thepredefined irregularities to be deployed in an actual luminanceenhancement substrate may comprise several types of irregularities(e.g., a combination of non-facet flat sections, in-kind or otherwise,and other irregularities that are neither in-kind nor non-facet flatsections).

The optical substrate may have a base portion (which may be unitary ormonolithic to the prism structure, which is equivalent to and havingsimilar characteristics as a separate underlying base layer), which hassufficient thickness to provide structural integrity to the finalluminance enhancement film.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and advantages of theinvention, as well as the preferred mode of use, reference should bemade to the following detailed description read in conjunction with theaccompanying drawings. In the following drawings, like referencenumerals designate like or similar parts throughout the drawings.

FIG. 1 schematically illustrates a sectional view of a prior artbrightness enhancement film.

FIG. 2 schematically illustrates the structure of an LCD having anoptical substrate, in accordance with one embodiment of the presentinvention.

FIG. 3 is a schematic perspective view of the structured light outputsurface of an optical substrate, in accordance with one embodiment ofthe present invention.

FIG. 4A is a schematic perspective view of the structured light outputsurface of an optical substrate, in accordance with another embodimentof the present invention; FIG. 4B is a sectional view taken along line4B-4B in FIG. 4A.

FIGS. 5A to 5C are sectional views of structured output surfaces ofoptical substrates, in accordance with further embodiments of thepresent invention.

FIGS. 6 and 7 are schematic plan views of the structured light outputsurfaces of optical substrates, in accordance with further embodimentsof the present invention.

FIG. 8 is a schematic view of an electronic device comprising an LCDpanel that incorporates the inventive optical substrate of the presentinvention, in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The present description is of the best presently contemplated mode ofcarrying out the invention. This invention has been described herein inreference to various embodiments and drawings. This description is madefor the purpose of illustrating the general principles of the inventionand should not be taken in a limiting sense. It will be appreciated bythose skilled in the art that variations and improvements may beaccomplished in view of these teachings without deviating from the scopeand spirit of the invention. The scope of the invention is bestdetermined by reference to the appended claims.

The present invention is directed to luminance enhancement substratehaving an optical substrate (which may be supported by a base layer)that possesses a structured surface that enhances luminance orbrightness and reduces the effects of structural defects on perceivedimage quality. In accordance with the present invention, userperceivable optical cosmetic defects caused by manufacturing or handlingcan be masked, largely reduced, or reduced in prominance by introducingdefined structural irregularities in the optical substrate, which may bein-kind to the anticipated defects.

The optical defect masking aspect of the present invention is applicableto various optical substrates having various types of structured lightoutput surfaces. The optical substrate may be in the form of a film,sheet, plate, and the like, which may be flexible or rigid, having a twoor three-dimensionally varying, structured light output surface thatcomprises a regular and/or irregular prism structure, and anon-structured, smooth, planar, light input surface. The prism structureat the light output surface may be viewed as comprising longitudinalregular and/or irregular prism and/or prism blocks arranged generallylaterally (side-by-side), defining peaks and valleys (a facet is definedbetween each adjacent peak and valley). In one embodiment, the lightoutput surface and the light input surface are generally parallel toeach other in the overall optical substrate structure (i.e., do not forman overall substrate structure that is generally tapered, concave, orconvex). In another embodiment, the optical substrate structure may beregular prism structure at the light output surface, which may be viewedas comprising side-by-side or lateral rows of regular prism blockswherein the peaks or valleys of adjacent rows of prism blocks may beparallel.

FIG. 2 illustrates an example of a flat panel display. A backlight LCD10, in accordance with one embodiment of the present invention,comprises a liquid crystal (LC) display module 12, a planar light sourcein the form of a backlight module 14, and a number of optical filmsinterposed between the LC module 12 and the backlight module 14. The LCmodule 12 comprises liquid crystals sandwiched between two transparentsubstrates, and control circuitry defining a two-dimensional array ofpixels. The backlight module 14 provides planar light distribution,either of the backlit type in which the light source extends over aplane, or of the edge-lit type as shown in FIG. 2, in which a linearlight source 16 is provided at an edge of a light guide 18. A reflector20 is provided to direct light from the linear light source 16 throughthe edge of the light guide 18 into the light guide 18. The light guideis structured (e.g., with a tapered plate and light reflective and/orscattering surfaces defined on the bottom surface facing away from theLC module 12) to distribute and direct light through the top planarsurface facing towards LC module 12. The optical films may include upperand lower diffuser films 22 and 24 that diffuse light from the planarsurface of the light guide 18. The optical films further include astructured surface optical substrate in accordance with the presentinvention, which redistributes the light passing through such that thedistribution of the light exiting the films is directed more along thenormal to the surface of the films. In the illustrated embodiment, thereare two structured optical substrates 26 and 28 (which may be similar)in accordance with the present invention, which are arranged with thelongitudinal prism structures generally orthogonal between the twosubstrates. The optical substrates 26 and 28 are often referred in theart as luminance or brightness enhancement films, light redirectingfilms, and directional diffusing films. The light entering the LC module12 through such a combination of optical films is uniform spatially overthe planar area of the LC module 12 and has relatively strong normallight intensity. The optical substrates in accordance with the presentinvention may be used with LCDs to be deployed for displays, forexample, for televisions, notebook computers, monitors, portable devicessuch as cell phones, PDAs and the like, to make the displays brighter.

Refer to FIG. 3, the brightness enhancement film 26 of the presentinvention includes an optical substrate 30 adhered to a support or baselayer 31. FIG. 3 (as well as the embodiments illustrated in the otherfigures) may schematically represent the features of a section of anoptical substrate 30 or an entire substrate 30. The optical substratehas a light input surface 32 that is planar and smooth, and a lightoutput surface 34 that has a prismatic structure that may be viewed ascomprising longitudinal regular prism blocks 35 arranged in lateral rows(i.e., side-by-side). A prism block 35 may be viewed as a building blockfor the optical substrate. It is noted that, as will be apparent in thediscussion herein below, the prism blocks 35 are connected to adjoiningprism blocks 35 in longitudinal and/or lateral directions. Because theprism blocks 35 are not in fact individual discrete blocks assembledtogether, the material of the prism blocks 35 are in a continuum orcontinuous monolithic structure, with no physical contact surfaces orjoining surfaces per se.

In one embodiment of the present invention, the light output surface 34and the light input surface 32 are generally parallel to each other inthe overall optical substrate structure (i.e., do not form an overallsubstrate structure that is generally tapered like a light guide platein a backlight module, or that is concave or convex). While FIG. 3 showsthe base 31 to be of uniform thickness, it may be non-uniform thickness.The end section of FIG. 3 when enlarge would look generally similar toFIG. 1, with the exception of the presence of any defects 40 orirregularities 42 discussed below.

The prism blocks 35 each has two longitudinal facets 33, or longitudinalflat surfaces, forming a longitudinal peak 36. The facets 33 ofadjoining prism blocks 35 intersect to define a valley 37. The facets 33are slanted with respect to the light input surface 32, which provideintended optical reflections and refractions in connection withluminance enhancement. The facets 33 are distinguished from non-facetsurfaces. Non-facet surfaces instead refer to flat structures generallyparallel to the light input surface 32, or facing generally in thez-direction (defined below). Non-facet surfaces may be unintendedstructural defects in the prismatic structure, which may arise frommanufacturing or handling, or intentionally introduced irregularitiesfor masking the optical defects caused by such original structuraldefects, as further discussed below.

For ease of reference, the following orthogonal x, y, z coordinatesystem would be adopted in explaining the various directions. As shownin FIG. 3, the x-axis is in the direction across the peaks and valleys,also referred to as the lateral direction. The y-axis is orthogonal tothe x-axis, in the plane of the substrate 30, in a generallylongitudinal direction of the prism blocks 35. The prism blocks may beregular or irregular (as disclosed in copending U.S. patent applicationSer. No. 11/450,145, commonly assigned to the assignee of the presentinvention, and is fully incorporated by reference herein). In theillustrated embodiment, the prism blocks 35 are regular in geometry. Thelight input surface 32 lies in an x-y plane. For a rectangular piece ofthe optical substrate, the x and y-axes would be along the orthogonaledges of the substrate 30. The z-axis is orthogonal to the x and y-axes.The edge showing the ends of the lateral rows of the prism blocks 35lies in the x-z plane, such as shown in FIG. 3. References to crosssections of a prism block 35 would be sections taken in x-z planes, atvarious locations along the y axis. Further, references to a horizontaldirection would be in an x-y plane, and references to a verticaldirection would be in the z-direction. Hereinafter, references toheights of peaks and valleys are measured in the z-direction withrespect to the interfacing planar surface between the adjoiningsubstrate 30 and base layer 31. It is noted that the references to peakvertex angles herein refer to the angles of the peak 36, and valleyvertex angles herein refer to the angles of the valleys 37, as viewedalong cross sections in the x-z planes at locations along the ydirection, as defined above.

In the illustrated embodiment, the prism blocks 35 are shown to besubstantially similar to one another, and have uniform cross-sectionsalong the longitudinal direction (y-axis). The peak vertex angles aresimilar (70 to 110 degrees), and the valley vertex angles are alsosimilar to one another (70 to 110 degrees). It is noted that in theillustrated sectional views in x-z planes, the peak vertex angles andthe valley vertex angles may be rounded instead of a sharp point, due tomanufacturing constraints. The height of the valleys 37 may vary in thelateral (x) direction of the respective valleys 37, and may also furthervary in the longitudinal (y) direction. The prism blocks may possess astructure having structure, geometry and features that are disclosed inearlier filed copending U.S. patent applications Ser. Nos. 11/450,145and 11/635,802, which have been commonly assigned to the assignee of thepresent invention, and which had been incorporated by reference herein.

There is a thin layer of material of thickness d (similarly shown inFIG. 1) below the valleys 37 in the optical substrate 30, which definesa valley bottom thickness or valley height above the top surface of thebase layer 31, except where structural defects 40 arose frommanufacturing or handling, and where irregularities 42 have beenintentionally introduced in accordance with the present invention. Thevalley bottom thickness could vary across the lateral direction orlongitudinal direction, from substantially zero thickness, to a definedthickness D (e.g., 0.3 to 10 micrometers), with the exception at thoselocations where defects 40 (from manufacturing and handling) andirregularities 42 (introduced in accordance with the present invention)cause the base layer 31 to be exposed without coverage of material ofthe optical substrate 30. In the illustrated embodiment in FIG. 3, theheights, or bottom thickness, of the valleys 37 are constant, withbottom thickness is D, with the exception of above noted defects 40 andirregularities 42. Only a few scattered defects 40 and irregularities 42are schematically illustrated in FIG. 3. The number, extent and coverageof the irregularities 42 to effectively mask optical defects perceivableby a user may be more than what is schematically illustrated in FIG. 3.

In the disclosed embodiments, the defects 40 are generally unintended,isolated, randomly generated (e.g., inherent from manufacturing and/orhandling), non-facet flat sections in the prism structure of the opticalsubstrate. For example, the non-facet flat sections may be present asflat-bottom valleys with a certain valley bottom thickness above thebase layer, and/or flat-top peaks, and/or openings in the light inputsurface 32 of the optical substrate which expose flat sections of theunderlying base layer. The non-facet flat sections of defects 40 may beof various shapes, geometries and sizes (e.g., longitudinal, or spots).The defects may be defined along valleys between adjacent prism blocksin the structured surface, either with adjacent facets extending to thetop surface of the base layer 31 to define a flat-bottom valley (i.e.,an opening at the light input surface 32, with the flat-bottom valleyfloor defined by the top surface of the underlying base layer 31), orfacets extending to a flat section of the optical substrate material (todefine a flat-bottom valley within the optical substrate 30), or with anopening extending through the valley bottom (the opening havinggenerally vertical sidewalls through the valley bottom). By nature ofdefects, the actual defects 40 present on a single optical substrate 30(and hence luminance enhancement film 26) may comprise a combination ofthe various forms of defects noted above, depending on the defectstypically encountered as a result of manufacturing processes andhandling. The defects 40 may be caused by molding defects, mold release,abrasion, scratches, etc.

In accordance with the present invention, perceivable optical cosmeticdefects caused by the structural defects in the optical substrate 30 canbe effectively masked from perception by distributing pre-definedstructural irregularities in the optical substrate 30, which may bein-kind to the anticipated defects. In one embodiment, theirregularities 42 may be in-kind to the anticipated defects, which takesimilar form (e.g., similar characteristic physical attributes) as thedefects 40. For example, the defects 40 can be masked by distributingintentionally introduced, in-kind, pre-defined non-facet flat sections(e.g., flat-bottom valleys, and/or flat-top peaks, and/or openingsexposing sections of underlying base layer), to diffuse the prominenceof the original defects with the introduced irregularities. The in-kindirregularities 42 introduced may not need to be of the exact same type,number, shape and size as the original defects 40, but share similarphysical attributes significant to masking those defects (e.g.,non-facet flat-sections). For example, openings (e.g., holes or gaps) inthe optical substrate 30 exposing flat sections of the underlying baselayer 31, or flat-bottom valleys, or flat-top peaks, may be masked by atleast one of flat-bottom valleys and/or flat-top peaks and/or openingsexposing flat sections of underlying base layer. The irregularitiesintroduced may be distributed across the optical substrate in anorderly, semi-orderly, random, or quasi-random manner.

The in-kind irregularities 42 intentionally introduced into the opticalsubstrate 30 may comprise non-facet flat sections of various forms, suchas in the form of openings defined in the light input surface 32 ofvarious shapes, geometries and sizes (e.g., longitudinal gaps, holesthat are elliptical, rhombus, oval, round, etc.), flat-bottom valleys,and/or flat-top peaks. The non-facet flat irregularities 42 may bedefined along valleys between adjacent prism blocks in the structuredsurface, either with adjacent facets extending to the top surface of thebase layer 31 to define a flat-bottom valley (i.e., an opening at thelight input surface 32, with the flat-bottom valley floor defined by thetop surface of the underlying base layer 31), or facets extending to aflat section of the optical substrate material (to define a flat-bottomvalley within the optical substrate 30), or with an opening extendingthrough the valley bottom (the opening having generally verticalsidewalls through the valley bottom). The non-facet flat irregularitiesmay range in width (in the x-direction) on the order of 0.5 to 200 μm,and range in length (in the y-direction) on the order of 1.0 μm to 500mm.

The irregularities introduced may be distributed across the opticalsubstrate in an orderly, semi-orderly, random, or quasi-random manner.

FIGS. 4A and 4B illustrate another specific embodiment of irregularities42, which take the form of flat-bottom valleys defined by longitudinal,narrow-band, non-facet flat irregularities extending substantially alongthe entire length of the valleys between adjacent prism blocks 35. (Itis noted that defects 40 are not shown in these and further figuresdiscussed below, to simplify illustration and discussion.) In theembodiment of FIGS. 4A and 4B, the width of the flat-bottom valleys isuniform along the valleys and the widths of the different valleys aresame. The width of the valleys may vary along the valleys. Further, thevalleys may vary in width and shape, as illustrated in FIGS. 5A-5C.

FIGS. 5A to 5C illustrate sectional views of other embodiments oflongitudinal irregularities 42, varying from the embodiment shown inFIG. 4. The irregularities 42 having flat bottom valleys may bedistributed every n prism blocks 35 (n may vary across the substrate).In the particular illustrated embodiment of FIG. 5A, an irregularity 42having a flat bottom valley of a particular width (e.g., same width forthe irregularities 42) is disposed every three prism blocks 35. Thevalleys 37 may have a valley bottom thickness D. FIG. 5B illustratesanother embodiment in which an irregularity 42 having a flat bottomvalley of a particular width (e.g., same width for the irregularities42) is disposed alternately every two to three prism blocks 35. In thisembodiment, valleys 37 may have a valley bottom of substantially zerothickness (i.e., the bottom of the valley is substantially coplanar withthe light input surface 32 or the top surface of the base layer 31).

While each of the above discussed embodiments illustrates a single typeof irregularities 42 uniformly distributed, the irregularities 42 maycomprise a combination of two of more types of intentionally introducedirregularities discussed above, which may be distributed in a random,quasi-random, orderly, or quasi-orderly manner.

FIG. 5C illustrates further varying distribution of irregularities 42.In FIG. 5C (which could be a sectional view at a particular y-locationof an optical substrate 30 as shown in FIG. 3). The valleys 37 a, 37 band 37 c have different valley bottom thicknesses. There is anirregularity 42 a having a non-facet flat section in the form offlat-bottom valley 37 d having a particular valley bottom thickness.There is also an irregularity 42 b having a non-facet flat section thatis defined by an opening extending through the valley 37 e presentbetween two adjacent prism blocks 35. Such opening has side wallsthrough the valley section. Irregularities 42 c and 42 d have flatbottom valleys 37 f and 37 g with different widths. The distributionvariation shown in FIG. 5C may be further varied across the entiresubstrate, or repeated across the entire substrate. For example, thewidth could range in the order of 1.5 to 200 μm. The distribution may ormay not be repeated within a range of 200 μm to 200 mm.

In another aspect of the present invention, in-kind irregularities areintroduced to optical substrates that have a two or three-dimensionallyvarying, structured light output surface that comprises an irregularprism structure, and a non-structured, smooth, planar, light inputsurface. In one embodiment of the present invention, the light outputsurface and the light input surface are generally parallel to each otherin the overall optical substrate structure (i.e., do not form an overallsubstrate structure that is generally tapered, concave, or convex). Theirregular prism structure at the light output surface may be viewed ascomprising longitudinal irregular prism blocks arranged laterally(side-by-side), defining peaks and valleys. A facet of the longitudinalirregular prism block is defined between each adjacent peak and valley.The longitudinally varying prismatic structure has one or more of thefollowing structural characteristics. At least a plurality of theirregular prism blocks have a large end tapering to a small end, or froma large width to a narrow width, or from a large peak height to a smallpeak height. Adjacent peaks, adjacent valleys, and/or adjacent peak andvalley are not parallel within at least a range of lateral prism blocks.The adjacent peaks, adjacent valleys, and/or peak and valley mayalternate from parallel to non-parallel in an orderly, semi-orderly,random, or quasi-random manner. Similarly, the non-parallel peaks,valleys and/or peak and valley may alternate between convergence todivergence in reference to a particular longitudinal direction, in anorderly, semi-orderly, random, or pseudo-random manner. All the peaks donot lie in the same plane, and all the valleys may or may not lie in thesame plane. The sections taken across the peaks and valleys in thelongitudinal direction are not constant. The pitch between adjacentpeaks, adjacent valleys, and/or adjacent peak and valley varieslaterally across the prism blocks in an orderly, semi-orderly, random,or quasi-random manner.

The irregular prism structure at the light output surface may also beviewed as comprising side-by-side or lateral rows of irregular prismblocks, wherein each longitudinal row of irregular prism blocks may beviewed as comprising a plurality of irregular prism blocks connected endto end in a continuous manner. In one embodiment, the smaller end of oneprism block is connected to the smaller end of another prism block alongthe same row, and the larger end of one prism block is connected to thelarger end of another prism block along the same row. The lateraladjacent peaks, adjacent valleys, and/or adjacent peak and valley arenot parallel. The peak and valley structure across the prism blocks mayhave further structural characteristics similar to the previousembodiment. The adjacent irregular prism blocks may be irregularlongitudinal sections having the same length, or random or quasi-randomirregular sections having different lengths. In yet another embodimentof the present invention, one or more facets of each prism blocksections may be substantially flat, or curved (convexly and/orconcavely).

The foregoing optical substrate structure has been discussed incopending U.S. patent application Ser. No. 11/450,145, which had beenincorporated by reference herein.

FIGS. 6 and 7 illustrate the top plan view of peaks and valleys of prismblocks having at least some of the above noted characteristics. (Note,in FIGS. 6 and 7, defects 40 are not shown to simplify illustration anddiscussion.) FIG. 6 represents the embodiment in which the irregularprism blocks are arranged in a zig-zag pattern. FIG. 7 represents theembodiment in which the irregular prism blocks are arranged to form acurved pattern. FIGS. 6 and 7 illustrate the top plan view of opticalsubstrate 30 of luminance enhancement film 26. In these figures, peaks36 and valleys 37 of the prism blocks 35 are not parallel (i.e., in alateral x-direction) over a range of laterally and/or longitudinallyadjoining prism blocks 35. Some of the valleys 37 and/or peaks 36 maynot lie in the same horizontal plane within the substrate, as the facetsof the prism blocks of one row intersect the facets of the prism blocksof another row, with the lines of intersection of the facets (i.e., thevalleys) at different heights from the light input surface 32, dependingin part on the width of the prism blocks. It is noted that in theembodiments of FIGS. 6 and 7, one prism block 35 intersect another prismblock 35 in both the longitudinal and lateral directions.

In the embodiment of FIG. 7, the peaks 36 and/or valleys 37, and/or thefacets 33 of one or more prism blocks 35 may be substantially curved(convex and/or concave) in the plane of the optical substrate 30. Thepeaks 36 and/or valleys 37 may follow wavy lines. The vertex angle ofthe peaks 36 of a wavy prism block may or may not have a constant angleat x-z plane sectional views along the y-direction. It is noted that oneither side of a peak 36, other than making both facets 33 curved, onefacet 33 may be curved and the other facet 33 may be flat. Differentpeaks 36 follow different curves, which may include a section of onlyone curvature, or many sections having different curvatures in a random,quasi-random, orderly or semi-orderly manner along a particular peak. Asshown in FIG. 7, adjoining prism blocks across the structured surfacemay have different curved or wavy peaks and/or facet surfaces, havingcurvatures differing in a random, quasi-random, orderly or semi-orderlymanner.

In both FIGS. 6 and 7, non-facet flat irregularities 42 are provided.Specifically for the specific embodiments illustrated, theirregularities 42 are in the form of flat-bottom valleys in alongitudinal gap form of a limited length between adjacent prism blocks35. The prism blocks 35 may or may not have different lengths ofsegment, different heights, different curvature, and different sizes atboth ends of a single prism and/or the prisms. The shapes of theseirregularities 42 are varied by the lengths, heights, curvatures andsizes of the prisms accordingly.

The irregularities are schematically shown to be distributed in a row ina lateral direction, but other distribution may be adopted, in a random,quasi-random, orderly or quasi-orderly manner. These additionalembodiments may have irregularities 42 that share features andcharacteristics of those irregularities discussed in connection withearlier embodiments.

As an example to illustrate the relative dimensions of an opticalsubstrate in accordance with the present invention, the peak heights areon the order of 10 to 200 micrometers, the valley heights (bottomthickness) are on the order of 0.3 to 10 micrometers, the thickness ofthe base layer 31 is on the order of 25 to 1000 micrometers. Theforegoing dimensions are intended to illustrate the fact that thestructured surface features are microstructures, in the micrometersrange. By way of example, the overall size of the area of the opticalsubstrate may vary on the order of 2 mm to 10 m in both width and length(and even larger dimensions possible), depending on the particularapplication (e.g., in a flat panel display of a cellular phone, or in asignificantly larger flat panel display of a TV monitor). Thecharacteristic size of the prism blocks on the structured surface of theoptical substrate need not change appreciably with different overalloptical substrate size.

The optical cosmetic defect masking effects of the intentionallyintroduced predefined irregularities would depend on at least one of thefollowing factors (e.g., relating to the non-facet flat sections, perunit area of the optical substrate, in relation to anticipated defects):(a) physical attributes, such as number, dimension, size, shape,geometry, types and combination of such physical attributes, (b)coverage of introduced irregularities, such as area, distributionpattern, mixture/combination of types of irregularities; (c)relationship of the irregularities to the anticipated structural defectsand the physical attributes and coverage thereof; and (d) the contrastand resolution of features (e.g., defects 40, irregularities 42, etc.)perceivable in an image (e.g., by the-naked eyes of an average person).Accordingly, such factors are taken into consideration when predefiningthe irregularities to be intentionally introduced into the opticalsubstrate. Concerning (d), it is noted that contrast of a feature, e.g.,a defect (e.g., non-facet flat section of a flat-bottom valley) inrelation to its surrounding areas in an image allow such feature to beperceivable by naked eyes (e.g., as a white spot). Further, when thereare sufficient irregularities distributed, the intended distribution ofdiscrete irregularities creates a more uniformed perception that reducesthe prominence of isolated defects. In addition, where the distancebetween two features is closer than the resolution of naked eyes, thenaked eyes may no longer be able to perceive and resolve the features asseparate and distinct. Therefore, more closely spaced irregularities mayfurther create a blended image appearance to mask or reduce perceivabledefects.

The purpose to distribute the irregularities is to appropriatelyallocate irregularities over the whole structured light output surface,so that when viewed by naked eyes, the whole surface would look like auniform plane. Each single irregularity should not be seen individually,because they are so small that they would not be perceived by thecapability of a viewer's eyes with respect to resolution or contrastbetween the areas with and without irregularity. The size of eachirregularity and the distances between adjacent irregularities either inlongitudinal (y) or on transverse (x) direction are defined also withthis purpose in mind. The structural irregularities should be insufficient presence to substantially mask at least small opticalcosmetic defects anticipated and/or typically encountered in themanufacturing process and/or subsequent handling, which would otherwisebe observable in the finished luminance enhancement film, and/or when ithas been placed into service in an LCD panel, to a person's naked eye.

For example, a number of scratched spots with a width about 9 μm and alength from 15 to 40 μm is lined up as a 500 μm (over 10 prisms) whiteline defect which could be masked by distributing non-facet flatsections with a width of about 5 μm and a length between 60 and 100 μmrandomly. All these scratched spot defects are blended together with theirregularities and provides a blended view that would be perceived asbeing more uniform in image quality.

The optical substrate 30 may be formed with an optically transparentmaterial, such as acrylic. The base substrate 31 may be of PET material,but may be made from the same transparent material as the opticalsubstrate 30, which provides additional structural support to therelatively thin optical substrate 30. The optical substrate 30 may beflexible enough to be manufactured in a roll, which is laid on andbonded to the separate base substrate 31. While the thickness of thebase substrate may be on the order of 25 to 1000 micrometers thick, thethickness of the base substrate may be thinner or thicker than thisrange, depending on the particular application. Generally, though notrequired, larger size optical substrate may have a thicker basesubstrate to provide better support, and a smaller size opticalsubstrate may require a thinner base substrate for smaller scaleapplications.

The predefined irregularities intentionally introduced into thestructured optical substrate 30 may be formed by prior art processes forforming microstructures on optical substrates, which are configured toprovide the predefined structural irregularities in accordance with thepresent invention. For example, the structured surface of opticalsubstrate of the present invention may be generated in accordance with anumber of process techniques, including micromachining using hard toolsto form molds or the like for the prismatic profile having thepredefined structural irregularities described above. The hard tools maybe very small diamond tools mounted on CNC (Computer Numeric Control)machines (e.g. turning, milling and ruling/shaping machines).Furthermore, known STS (Slow Tool Servo) and FTS (Fast Tool Servo) areexamples of the devices. U.S. Pat. No. 6,581,286, for instance,discloses one of the applications of the FTS for making grooves on anoptical film by using thread cutting method. To provide predefinedstructural irregularities, these machines may include certainperturbation means to assist the tools moving with small shifts andmaking prisms, and hence non-facet flat irregularities having differentlevels of irregularities. Known STS, FTS may include ultrasonicvibration apparatus to provide perturbation or vibration to accomplishstructural irregularities predefined in the mold. By using the devicesto form surfaces in the mold in relation to increasing degrees offreedom, three-dimensionally varying regular and/or irregular prisms andflats of the structured surfaces of the optical substrates disclosedabove can be obtained.

The master may be used to mold the optical substrate directly or used inelectroforming a duplicate of the master, which duplicate is used tomold the optical substrate. The mold may be in the form of a belt, adrum, a plate, or a cavity. The mold may be used to form the prismaticstructure on a substrate through hot embossing of the substrate, and/orthrough the addition of an ultraviolet curing or thermal settingmaterials in which the structures are formed. The mold may also be usedto form the optical substrate through injection molding. The substrateor coating material may be any organic, inorganic or hybrid opticallytransparent material and may include suspended diffusion, birefringentor index of refraction modifying particles.

While the foregoing embodiments are illustrated and discussed to includean optical substrate 30 supported by a separate base layer 31, it iswithin the scope and spirit of the present invention that the base layer31 is not present, but the optical substrate may have a base portionwhich may be unitary or monolithic to the prism blocks 35 in thestructured surface (i.e., formed from the same piece of material). Suchbase portion would be equivalent to, in place of, and share similarcharacteristics as, the separate base layer 31 discussed above. One canview an optical substrate having a unitary base portion to be comprisinga prism structured layer and an adjoining base layer, wherein such twolayers are in a continuum, monolithic structure. Further, a separatebase layer may be provided in addition to such base portion. The baseportion, and/or base layer, should be of sufficient thickness to providestructural integrity to the final luminance enhancement film.

While the anticipated defects 40 and predefined irregularitiesintentionally introduced are described as non-facet flat sections in theillustrated embodiments herein (discussed above and to be discussedbelow), if the anticipated defects in the optical substrate are otherthan non-facet flat sections, the in-kind irregularities intentionalintroduced into the optical substrate would likewise take on in-kindattributes other than non-facet flat sections.

While the above-illustrated embodiments refer to intentionallyintroducing predefined in-kind irregularities to mask anticipateddefects, in another aspect of the present invention, the irregularitiesintroduced need not be in-kind to all the defects. Regardless of defectsanticipated, the irregularities introduced may simply be predefinednon-facet flat sections (e.g., flat-bottom valleys, and/or flat-toppeaks, and/or openings exposing sections of underlying base layer). Thismay still mask defects beyond non-facet flat section defects found onthe prism structure of the optical substrate created by, such as, forexample, scratches, cutting marks, cracks, indentations and/or otherunintended structural defects in the prism structure, and/or foreignparticles or materials introduced during molding process, which may ormay not be subsequently released from the prism structure. The defectsmay be found anywhere on the prism structure (e.g., prism peaks, valleyand/or facets, and/or underlying layer, if present, which supports theoptical substrate).

The predefined irregularities introduced may not mask all types ofdefects present in an actual luminance enhancement substrate. Thepredefined irregularities to be deployed in an actual luminanceenhancement substrate may comprise several types of irregularities,including non-facet flat sections, in-kind or otherwise, and/or otherirregularities that are neither in-kind nor non-facet flat sections, ora combination of the foregoing.

Further, the following variations are well within the scope and spiritof the present invention. The peak and valley vertex angles may or maynot vary across laterally adjoining rows. It is noted that thegeometries (e.g., overall size, peak and valley angles, etc.) may bedifferent for different prism blocks 35 in the optical substrate 30. Thepitch between adjacent peaks 36, adjacent valleys 37, and/or adjacentpeak 36 and valley 37 may vary in an orderly, semi-orderly, random, orquasi-random manner. It is noted that an array, pattern or configurationof a group of random irregular prism blocks may repeat over a range ofarea or length over the overall structured light output surface of theoptical substrate 30, resulting in an overall orderly, semi-orderly orquasi-random pattern or arrangement for the overall optical substrate.Adjacent peaks, adjacent valleys, and/or adjacent peak and valley may ormay not be parallel within at least a range of lateral prism blocks. Theadjacent peaks 36, adjacent valleys 37, and/or adjacent peak 36 andvalley 37 may alternate from parallel to non-parallel, in an orderly,semi-orderly, random, or quasi-random manner. Similarly, adjacentnon-parallel peaks 36, adjacent valleys 37 and/or adjacent peak 36 andvalley 37, may alternate between convergence to divergence (in referenceto the same general longitudinal direction of the prism blocks), in anorderly, semi-orderly, random, or pseudo-random manner. Sections of theoptical substrate 30 taken across the peaks 36 and valleys 37 in an x-zplane at various locations along the y-direction and/or in a generallongitudinal direction of a particular peak or valley may or may not beconstant.

In accordance with the present invention, the optical substratecomprises a prismatic, structured light output surface havingpredefined, intentionally introduced irregularities, which enhancesbrightness and masks otherwise user perceivable optical cosmeticdefects, when applied in an LCD for example. An LCD incorporating theinventive optical substrate in accordance with the present invention maybe deployed in an electronic device. As shown in FIG. 8, an electronic110 (which may be one of a PDA, mobile phone, television, displaymonitor, portable computer, refrigerator, etc.) comprises the inventiveLCD 10 (FIG. 2) in accordance with one embodiment of the presentinvention. The LCD 10 comprises the inventive optical substratedescribed above. The electronic device 110 may further include within asuitable housing, a user input interface such as keys and buttons(schematically represented by the block 116), image data controlelectronics, such as a controller (schematically represented by block112) for managing image data flow to the LCD panel 10, electronicsspecific to the electronic device 110, which may include a processor,A/D converters, memory devices, data storage devices. etc.(schematically collectively represented by block 118), and a powersource such as a power supply, battery or jack for external power source(schematically represented by block 114), which components are wellknown in the art.

While particular embodiments of the invention have been described hereinfor the purpose of illustrating the invention and not for the purpose oflimiting the same, it will be appreciated by those of ordinary skill inthe art that numerous variations of the details, materials, andarrangements of parts may be made without departing from the scope ofthe invention as defined in the appended claims.

1. A method of making a luminance enhancement substrate, comprisingforming an optical substrate, wherein the optical substrate comprises aplanar light input surface at one side of the optical substrate, and astructured light output surface at an opposite side of the opticalsubstrate, wherein predefined structural irregularities distributed inthe structured light output surface are formed in the optical substrate,whereby certain user perceivable structural defects that have beenunintentionally included in the optical substrate can be masked by thestructural irregularities, wherein the structured light output surfacecomprises prismatic structures defined by facets, and wherein thestructural irregularities comprise a structure corresponding to anon-facet flat section.
 2. The method of making a luminance enhancementsubstrate as in claim 1, wherein the structural defects comprisenon-facet flat sections in the structured light output surface, andwherein the structure of the structural irregularities comprises anin-kind structure to the structural defects.
 3. The method of making aluminance enhancement substrate as in claim 1, wherein the opticalsubstrate is formed by a molding process, wherein the mold is formed bypredefining structural irregularities in a surface in the mold whichcorresponds to the structured light output surface, whereby thestructural irregularities are intentionally introduced to the opticalsubstrate formed by the molding process.
 4. A method of making aluminance enhancement substrate, comprising forming an opticalsubstrate, wherein the optical substrate comprises a planar light inputsurface at one side of the optical substrate, and a structured lightoutput surface at an opposite side of the optical substrate, whereinpredefined structural irregularities distributed in the structured lightoutput surface are formed in the optical substrate, whereby certain userperceivable structural defects that have been unintentionally includedin the optical substrate can be masked by the structural irregularities,wherein the structured light output surface comprises valleys and peaks,and wherein the structure of the structural irregularities correspondsto a flat-bottom valley.
 5. The method of making a luminance enhancementsubstrate as in claim 4, wherein the optical substrate is formed by amolding process, wherein the mold is formed by predefining structuralirregularities in a surface in the mold which corresponds to thestructured light output surface, whereby the structural irregularitiesare intentionally introduced to the optical substrate formed by themolding process.
 6. The method of making a luminance enhancementsubstrate as in claim 5, wherein the structural irregularities arepredefined in the mold in anticipation of structural defects that areinherent in the molding process and/or subsequent handling of theoptical substrate.
 7. The method of making a luminance enhancementsubstrate as in claim 6, wherein the structural irregularities arepredefined in the mold based on consideration of one or more of thefollowing factors relating to the structural irregularities in relationto anticipated defects, per unit area of the optical substrate: (a)physical attributes, such as number, dimension, size, shape, geometry,types and combination of such physical attributes, (b) coverage ofintroduced irregularities, such as area, distribution pattern,mixture/combination of types of irregularities; (c) relationship of theirregularities to the anticipated defects and the physical attributesand coverage thereof; and (d) contrast and resolution of defects andirregularities perceivable in an image by the naked eyes of an averageperson; and wherein the structural irregularities are in sufficientpresence in the structured light output surface to substantially mask atleast small structural defects anticipated and/or typically encounteredin the molding process and/or subsequent handling, which would otherwisebe observable in the finished luminance enhancement substrate, and/orwhen it has been placed into service in an LCD panel, to a person'snaked eye.
 8. The method of making a luminance enhancement substrate asin claim 4, further comprising a base layer supporting the light inputsurface of the optical substrate, wherein the structure of thestructural irregularities corresponding to a flat-bottom valley isdefined by at least one or (a) an opening in the light input surfaceexposing the base layer, and (b) a flat-bottom valley having a valleybottom thickness above the base layer.
 9. The method of making aluminance enhancement substrate as in claim 4, wherein the structuraldefects comprise a structure corresponding to at least one of aflat-bottom valley and a flat-top peak.
 10. The method of making aluminance enhancement substrate as in claim 9, further comprising a baselayer supporting the light input surface of the optical substrate,wherein the structure of the structural irregularities corresponding toa flat-bottom valley is defined by at least one or (a) an opening in thelight input surface exposing the base layer, and (b) a flat-bottomvalley having a valley bottom thickness above the base layer.
 11. Themethod of making a luminance enhancement substrate as in claim 4,wherein the structural irregularities comprise an in-kind structure tothe structural defects.
 12. The method of making a luminance enhancementsubstrate as in claim 11, wherein the structured light output surfacecomprises prismatic structures defined by facets, and wherein thestructural irregularities comprises a structure corresponding to anon-facet flat section.
 13. The method of making a luminance enhancementsubstrate as in claim 4, wherein the structural irregularities aredistributed across the optical substrate in at least one of orderly,semi-orderly, random, and quasi-random manner.
 14. The method of makinga luminance enhancement substrate as in claim 4, wherein the structuralirregularities comprise at least one of an in-kind structure to thestructural defects, a structure comprising a non-facet flat section, anda combination thereof.
 15. The method of making a luminance enhancementsubstrate as in claim 4, further comprising a base layer supporting thelight input surface of the optical substrate.
 16. The method of making aluminance enhancement substrate as in claim 4, wherein the structuredlight output surface comprises prismatic structures defined by facets,wherein the prismatic structures comprises prisms that are similaracross the structured light output surface.
 17. The method of making aluminance enhancement substrate as in claim 16, wherein the prismscomprise regular prisms, or prisms symmetrical about a longitudinaldirection.
 18. A method of enhancing brightness of an image rendered bya flat panel display, comprising: providing a display module that emitslight in accordance with an image; and providing a luminance enhancementsubstrate comprising an optical substrate made by the method as in claim4, whereby brightness of the image is enhanced by the structured lightoutput surface.
 19. A method of making a flat panel display, comprising:providing a display module emitting light in accordance with an image;and providing a luminance enhancement substrate comprising an opticalsubstrate made by the method as in claim 4, whereby brightness of theimage is enhanced by the structured light output surface.
 20. A methodof making a luminance enhancement substrate, comprising forming anoptical substrate, wherein the optical substrate comprises a planarlight input surface at one side of the optical substrate, and astructured light output surface at an opposite side of the opticalsubstrate, wherein predefined structural irregularities distributed inthe structured light output surface are formed in the optical substrate,whereby certain user perceivable structural defects that have beenunintentionally included in the optical substrate can be masked by thestructural irregularities, wherein the structured light output surfacecomprises valleys and non-flat top peaks, and wherein the structure ofthe structural irregularities corresponds to a flat-top peak.